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United States Patent |
6,013,961
|
Sakamaki
,   et al.
|
January 11, 2000
|
Electric motor having rotation detection sensor
Abstract
In an electric motor having a rotation detection sensor, a pair of
engagement recesses are provided on an axial end surface of a resin
cylindrical body of a commutator. A permanent magnet is held around a
rotary shaft of the motor with its one axial end surface being in abutment
with the axial end surface of the cylindrical body. A pair of engagement
recesses is provided on the other axial end surface of the magnet. A resin
busing having a cylindrical part and a disk part is fitted on the rotary
shaft at the side of the other axial end surface of the magnet. A pair of
engagement protrusions is formed on the cylindrical part to be engaged
with the engagement recesses of the cylindrical body, thereby restricting
a relative movement between the bushing and the cylindrical body. Further,
a pair of engagement protrusions is formed on the disk part to be engaged
with the engagement recesses of the magnet, thereby restricting a relative
movement between the bushing and the magnet. Thus, the magnet of the
rotation sensor is fixedly mounted around the rotary shaft without using
an adhesive bond.
Inventors:
|
Sakamaki; Ryousuke (Toyohashi, JP);
Ohishi; Masanori (Hamamatsu, JP);
Tsuda; Hirokazu (Toyohashi, JP)
|
Assignee:
|
Asmo Co., Ltd. (Shizuoka-pref, JP)
|
Appl. No.:
|
258092 |
Filed:
|
February 24, 1999 |
Foreign Application Priority Data
| Mar 18, 1998[JP] | 10-068472 |
Current U.S. Class: |
310/68B; 310/177 |
Intern'l Class: |
H02K 011/00 |
Field of Search: |
310/68 B,67 R,177,40 MM
324/174
|
References Cited
U.S. Patent Documents
3570116 | Mar., 1971 | Armstrong et al. | 29/596.
|
3796899 | Mar., 1974 | Giachello | 310/156.
|
4110676 | Aug., 1978 | Edick et al. | 322/31.
|
4259603 | Mar., 1981 | Uchiyama et al. | 310/68.
|
4499420 | Feb., 1985 | Shiraki et al. | 324/174.
|
4857784 | Aug., 1989 | Mukaekubo | 310/68.
|
4935652 | Jun., 1990 | Maxa | 310/68.
|
5079468 | Jan., 1992 | Sata | 310/168.
|
5184038 | Feb., 1993 | Matsui et al. | 310/42.
|
5565721 | Oct., 1996 | Knappe | 310/68.
|
5717268 | Feb., 1998 | Carrier et al. | 310/156.
|
Foreign Patent Documents |
0 359 853 B1 | ., 1988 | EP.
| |
057767 A1 | Jun., 1993 | EP.
| |
5-161314 | ., 1993 | JP.
| |
5-199724 | Aug., 1993 | JP.
| |
6-74074 U | ., 1994 | JP.
| |
6-29374 U | ., 1994 | JP.
| |
6-217497 | Aug., 1994 | JP.
| |
6-327195 | Nov., 1994 | JP.
| |
Primary Examiner: Ramirez; Nestor
Assistant Examiner: Waks; Joseph
Attorney, Agent or Firm: Fish & Richardson P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese
Patent Application No. 10-68472 filed on Mar. 18, 1998.
Claims
What is claimed is:
1. An electric motor comprising:
a stator;
a rotary shaft supported rotatably by the stator;
a commutator fixedly supported on the rotary shaft;
a rotation detection sensor having a rotary member, wherein one axial end
surface of the rotary member faces one axial end surface of the
commutator; and
a bushing disposed on a side of another axial end surface of the rotary
member and having a part extending axially from one axial end surface
thereof and engaged with the commutator directly to sandwich the rotary
member therebetween.
2. An electric motor of claim 1, wherein the bushing includes:
a cylindrical part fitted around the rotary shaft and supporting the rotary
member thereon;
a first engagement part formed on one axial end surface of the cylindrical
part and engaged with the one axial end surface of the commutator to
restrict a relative rotation between the cylindrical part and the
commutator;
a disk part extending radially from another axial end surface of the
cylindrical part and abutting the another axial end surface of the rotary
member; and
a second engagement part formed on the disk part and engaged with the
rotary member to restrict a relative rotation between the disk part and
the rotary member.
3. An electric motor of claim 1, wherein the bushing includes:
a cylindrical part fitted around the rotary shaft and supporting the rotary
member thereon;
a first engagement part formed on one axial end surface of the cylindrical
part and engaged with the one axial end surface of the commutator to
restrict a relative rotation between the cylindrical part and the
commutator;
a disk part extending radially from another axial end surface of the
cylindrical part and abutting another axial end surface of the rotary
member; and
a second engagement part formed on the cylindrical part and engaged with
the rotary member to restrict a relative rotation between the disk part
and the rotary member.
4. An electric motor of claim 2, wherein:
the first engagement part is a tapered protrusion; and
the commutator has a tapered recess on the one axial end surface thereof to
receive the tapered protrusion therein.
5. An electric motor of claim 2, further comprising:
a bearing fitted in a holder to support the rotary shaft therein and held
in slidable contact with the disk part in an axial direction.
6. An electric motor of claim 3, wherein:
the first engagement part is a tapered protrusion; and
the commutator has a tapered recess on the one axial end surface thereof to
receive the tapered protrusion therein.
7. An electric motor of claim 3, further comprising:
a bearing fitted in holder to support the rotary shaft therein and held in
slidable contact with the disk part in an axial direction.
8. An electric motor of claim 2, wherein the bushing includes:
a raised part extending from one of the disk part and the cylindrical part
to press the rotary member resiliently to the commutator.
9. An electric motor of claim 3, wherein the bushing includes:
a raised part extending from one of the disk part and the cylindrical part
to press the rotary member resiliently to the commutator.
10. An electric motor of claim 1, wherein the bushing includes:
a first engagement part extending in an axial direction through the rotary
member and fixedly engaged with the commutator to restrict a relative
rotation between the bushing and the commutator; and
a second engagement part fixedly engaged with the rotary member to restrict
a relative rotation between the bushing and the rotary member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric motor having a rotation
detection sensor and, more particularly, to an improvement in mounting a
rotary member of a rotation detection sensor on a motor rotary shaft.
2. Related Art
It is known to provide a rotation detection sensor in an electric motor. As
shown in FIG. 22, this type of motor 21 has an annular permanent magnet 24
fixed around a rotary shaft 23 of an armature 22, so that it operates as a
rotary member of the rotation detection sensor. The magnet 24 is bonded to
a metal bushing 25 by an adhesive bond, and press-fitted on the rotary
shaft 23 together with the bushing 25.
This arrangement requires a high press-fitting precision, so that the
busing 25 is fitted fixedly on the rotary shaft 23. That is, a through
hole 25a of the bushing 25 and the rotary shaft 23 must be machined with
high precision. Further, it is necessary to bond the magnet 24 and the
bushing 25, and to dry the adhesive bond thereafter.
Further, a resin washer 27 is disposed between the magnet 24 and a bearing
26 supporting one end of the rotary shaft 23 therein, thereby preventing
the magnet 24 from sliding on the bearing 26 directly. This results in
increases in the number of component parts, in the number of production
processes, and in production cost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electric
motor having a rotation detection sensor, which can be produced with less
number of component parts and less number of production processes to
reduce production cost.
According to the present invention, an electric motor has a rotation
detection sensor, a permanent magnet of which is mounted on a rotary shaft
supporting thereon an armature and a commutator. A bushing is mounted on
the rotary shaft between a bearing and the magnet. The bushing is shaped
to directly engage with the commutator, sandwiching the permanent magnet
tightly therebetween.
Preferably, a pair of engagement recesses is provided on an axial end
surface of a resin cylindrical body of the commutator. A pair of
engagement recesses is provided on the magnet. The bushing is in an
integral unit of a cylindrical part and a disk part extending from the
cylindrical part. A pair of engagement protrusions is formed on the
cylindrical part to be engaged with the engagement recesses of the
cylindrical body, thereby restricting a relative movement between the
bushing and the cylindrical body. Further, a pair of engagement
protrusions is formed on the disk part to be engaged with the engagement
recesses of the magnet, thereby restricting a relative movement between
the bushing and the magnet. Thus, the magnet of the rotation sensor is
fixedly mounted around the rotary shaft without using an adhesive bond.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present invention will be
made more understandable by the following detailed description made with
reference to the accompanying drawings, throughout which the same or
similar reference numerals designate the same or similar component parts.
In the drawings:
FIG. 1 is a schematic sectional view showing an electric motor according to
an embodiment of the present invention;
FIG. 2 is an enlarged view showing a part of the motor shown in FIG. 1;
FIG. 3 is a perspective view showing component parts of the motor before
assembling;
FIG. 4 is a side view showing the component parts shown in FIG. 3;
FIG. 5 is a front view showing a bushing viewed in the direction V in FIG.
4;
FIG. 6 is a side view showing component parts used in a modified embodiment
of the present invention;
FIG. 7 is a front view showing a bushing viewed in the direction VII in
FIG. 6;
FIG. 8A is a perspective view showing a bushing used in a modified
embodiment of the present invention;
FIGS. 8B to 8G are perspective views showing engagement protrusions used in
modified embodiments;
FIG. 9 is a perspective view showing component parts used in a modified
embodiment of the present invention;
FIG. 10 is a perspective view showing the component parts used in the
modified embodiment of the present invention;
FIG. 11 is a perspective view showing the component parts used in the
modified embodiment of the present invention;
FIG. 12 is a perspective view showing a bushing used in a modified
embodiment of the present invention;
FIG. 13 is a sectional view showing the bushing shown in FIG. 12;
FIG. 14 is a perspective view showing a bushing used in a modified
embodiment of the present invention;
FIG. 15 is a sectional view showing the bushing shown in FIG. 14;
FIG. 16 is a perspective view showing component parts used in a modified
embodiment of the present invention;
FIGS. 17A and 17B are a plan view and a sectional view showing a bushing
shown in FIG. 16;
FIG. 18 is a perspective view showing component parts used in a modified
embodiment of the present invention;
FIG. 19 is a perspective view showing component parts used in a modified
embodiment of the present invention;
FIG. 20 is a perspective view showing component parts used in a modified
embodiment of the present invention;
FIG. 21 is a perspective view of a bushing and a commutator used in a
modified embodiment of the present invention; and
FIG. 22 is a schematic sectional view showing a conventional electric motor
.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIGS. 1 and 2, an electric motor 1 has a cylindrical
stator (yoke and permanent magnets) 2 and a holder 3a of a rotation
detection sensor 3. The motor 1 may be used to drive a power seat in a
vehicle in such a manner that the rotation detection sensor 3 detects
motor rotation which represents a power seat position. An armature 4
having a rotary shaft 5 is disposed within the stator 2 and the holder 3a.
The rotary shaft 5 is supported rotatably by bearings 6, 7. A commutator 8
is fixed on the rotary shaft 5 through a cylindrical body 9 made of resin.
As shown in FIGS. 3 and 4, the cylindrical body 9 has a pair of engagement
recesses 9b on its one axial side surface 9a, which is axially opposite to
the armature 4. The recesses 9b are provided symmetrically to face each
other in the radial direction with respect to the rotary shaft 5. A
permanent magnet 10, which is a rotary member of the rotation detection
sensor 3, is disposed to abut with the axial end surface 9a.
The magnet 10 is formed into an annular shape having a through hole 1a with
its one half and the other half being magnetized into N-pole and S-pole
respectively. A pair of engagement recesses 10d are formed on an axial end
surface 10c, which is axially opposite to the other axial end surface 10b
abutting the end surface 9a of the cylindrical body 9. The recesses 10d
are provided symmetrically to face each other in the radial direction with
respect to the rotary shaft 5. The magnet 10 is fitted on a resin bushing
11 disposed between the cylindrical body 9 and the bearing 6.
The bushing 11 is formed to have a cylindrical part 11c, on which the
magnet 10 is fitted, and a flange disk part 11a extending from the
cylindrical part 11c. The cylindrical part 11c has a through hole 11e, in
which the rotary shaft 5 is press-fitted. A pair of engagement protrusions
lid are formed on one axial end surface 11b of the disk part 11a. The
protrusions lid are provided symmetrically to face each other in the
radial direction with respect to the rotary shaft 5. Each protrusion 11d
has a square shape in section as shown in FIG. 4. A pair of engagement
protrusions 11g are formed on one axial end surface 11f of the cylindrical
part 11c. The protrusions 11g are provided symmetrically to face each
other in the radial direction with respect to the rotary shaft 5. Although
not shown, ribs may be formed on the axial end surface of the disk part
11a, which abuts with the bearing 6, so that the contact area between the
disk part 11a and the bearing 6 may be reduced to reduce a friction loss.
In this embodiment, the height d1 of each protrusion 11d is slightly less
than the depth d2 of each recess 10d, while the circumferential width of
each the protrusions 11d and that of each recess 10d are the same. Thus,
the protrusions 11d and recesses 10d are engaged tightly without backlash.
The height h1 of the cylindrical part 11c is slightly less than the
thickness h2 of the magnet 10. The diameter of the through hole 11e is so
set as to fit on the rotary shaft 5. The outer diameter of the cylindrical
part 11c is the same as the diameter of the through hole of the magnet 10.
The height d3 of each protrusion 11g is slightly less than the depth d4 of
each recess 9b of the cylindrical body 9. The circumferential width of
each protrusion 11g and that of each recess 9b are the same. Thus, the
protrusions 11g are engaged tightly with the recesses 9b without backlash.
The protrusions 11g are displaced 90.degree. from the protrusions 11d in
the circumferential direction as shown in FIG. 5.
In assembling the magnet 10 on the rotary shaft 5, the cylindrical part 11c
of the busing 11 is inserted first into the through hole 10a of the magnet
10 so that the protrusions 11d of the bushing 11 fits in the recesses 10d
of the magnet 10. Next, the bushing 11 fitted with the magnet 10 is
press-fitted on the rotary shaft 5, while engaging the protrusions 11g of
the busing 11 into the recesses 9b of the cylindrical body 9. Thus, the
magnet 10 is sandwiched between the cylindrical body 9 and the bushing 11
with its axial end surfaces 10b and 10c abut with axial end surface 9a of
the cylindrical body 9 and the axial end surface 11b of the bushing 11,
respectively.
According to the above embodiment, the following advantages are provided.
(1) The engagement of the protrusions 11g of the bushing 11 with the
recesses 9b of the cylindrical body 9 restricts a relative circumferential
movement between the busing 11 and the rotary shaft 5 of the armature 4.
The engagement of the protrusions 11d of the busing 11 with the recesses
10d of the magnet 10 restricts a relative circumferential movement between
the bushing 11 and the magnet 10. Thus, the magnet 10 is held fixedly on
the rotary shaft 5 and is sandwiched between the commutator 8 and the
bushing 11. As a result, the magnet 10 can be fitted around the rotary
shaft 5 fixedly in both circumferential and axial directions. That is,
high precision in press-fitting the bushing 11 on the rotary shaft and in
machining the bushing 11 and the rotary shaft 5 is not required, resulting
in reduction in production cost. Further, as the magnet 10 need not be
bonded to the bushing 11, the assembling process is simplified.
(2) As the bushing 11 is interposed between the bearing 6 and the magnet
10, the magnet 10 does not wear nor is damaged by the bearing 6.
(3) As the height h1 is slightly less than the thickness h2 and the height
d3 is slightly less than the depth d4, the end surfaces 10b and 10c of the
magnet 10 contact the end surfaces 9a and 11b directly, respectively. This
contact also restricts the magnet 10 from backlashing in both axial and
radial directions, thereby reducing backlash noise.
The above embodiment may be modified as follows.
(1) The diameter of the through hole 11e may be set to allow loose fitting
of the bushing 11 around the rotary shaft 5. In this instance, the
protrusions 11g of the bushing 11 or the recesses 9b of the cylindrical
body 9 should be changed to provide a press-fitting therebetween.
(2) The recesses 10d of the magnet 10 and the protrusions 11d of the
bushing 11 may be changed to protrusions and recesses, respectively.
(3) The protrusions 11d and the protrusions 11g of the bushing 11 may be
spaced apart from each other in the range of 0.degree. to 360.degree.
other than 90.degree..
(4) The height h1 of the cylindrical part 11c of the bushing 11 may be
slightly greater than the thickness h2 of the magnet 10. In this instance,
as shown in FIGS. 6 and 7, a recess 9c should be formed on the end surface
9a of the cylindrical body 9, and recesses 9b should be formed on the
bottom of the recess 9c. Further, the depth h3 of the recess 9c should be
greater than the height difference (h1-h2).
(5) The protrusions 11d of the bushing 11 may be changed to various shapes
shown in FIGS. 8A to 8G. In this instance, the recesses 10d of the magnet
10 should be changed to corresponding shapes to receive the protrusions
11d therein.
(6) The protrusions 11d of the bushing 11 and the recesses 10d of the
magnet 10 may be obviated as shown in FIG. 9. Specifically, the
cylindrical part of the bushing 11 is formed with a pair of grooves 11h,
and the magnet 10 is formed with a pair of protrusions 10e extending
radially inwardly to engage with the grooves 11h. The radial extension of
each protrusion 10e should be limited not to contact the rotary shaft 5.
As shown in FIGS. 10 and 11, the protrusions 10e may be provided only
partially in the axial direction of the magnet 10, that is, only at the
side of one of the end surfaces 10c and 10b, respectively. In the case of
FIG. 11, the axial length of each groove 11h may be greater than the axial
length of each protrusion 10e. Each protrusion 10e of the magnet 10 may be
formed into any shapes other than a square.
(7) Further, as shown in FIGS. 12 and 13, the bushing 11 may be formed with
a pair of raised parts 11i, which extend from the disk part 11a toward the
magnet 10. In this instance, the resiliency of the raised parts 11i keeps
biasing the magnet 10 toward the cylindrical body 9, thereby restricting
backlash of the magnet 10 in the axial direction.
(8) Alternatively, as shown in FIGS. 14 and 15, the bushing 11 may be
shaped to have a pair of raised parts 11j, which extends from the
cylindrical part 11c toward the disk part 11a. According to this
modification, the resiliency of the raised parts 11j keeps biasing the
magnet 10 toward the cylindrical body 9, thereby restricting backlash of
the magnet 10 in both axial and radial directions.
(9) Further, as shown in FIGS. 16, 17A and 17B, the cylindrical body 9 may
be shaped to have three recesses 9b at equal angular intervals on its end
surface 9a. the magnet 10 has no protrusions nor recesses thereon. The
bushing 11 is shaped to have three arcuate through holes 11m at equal
angular intervals. Each through hole 11m is formed around the outer
circumference of the cylindrical part 11c at a position where the
cylindrical part 11c extends from the disk part 11a. Three grooves 11n are
formed on the inner peripheral surface of the cylindrical part 11c at
positions radially inside of the through holes 11m. Each groove 11n
extends in the axial direction and has a triangular shape in section.
Three protrusions 11p are formed on the outer circumferential surface of
the cylindrical part 11c at positions radially outside of the grooves 11n.
Each protrusion 11p extends axially and has a triangular shape. Three
protrusions 11g are formed on the end surface 11f of the cylindrical part
11c at equal angular intervals. Each protrusion 11g is positioned between
adjacent two of the through holes 11m. Thus, when the cylindrical part 11c
of the bushing 11 is inserted into the through hole 10a of the magnet 10,
the magnet 10 is resiliently supported around the cylindrical part 11c due
to resiliency of the protrusions 11p. Thus, relative movement between the
magnet 10 and the bushing 11 is restricted.
(10) The disk part 11a of the bushing 11 may be shaped into a plurality of
ribs, which extend radially and arcuately from the cylindrical part 11c as
shown in FIG. 18.
(11) The cylindrical part 11c of the bushing 11 may be shaped into a
plurality of arcuate parts, each extending in the radial direction from
the disk part 11a.
(12) The bushing 11 may be shaped to have a plurality of raised parts 11r
extending toward the magnet 10 from the end surface of the disk part 11a
facing the magnet 10 as shown in FIG. 20. According to this modification,
the magnet 10 is held pressed to the cylindrical body 9 by the resiliency
of the raised parts 11r, so that the axial backlash of the magnet 10 is
restricted.
(13) Still further, as shown in FIG. 21, each protrusion 11g of the bushing
11 may be chamfered into a taper end 11s. Each recess 9b on the
cylindrical body 9 should be formed also into the taper shape in
correspondence with the taper end 11s. This will enable smooth engagement
of the protrusion 11g into the recess 9b. The shape of each protrusion 11g
may be hemispherical, conical or the like, while each recess 9b should be
in a corresponding shape.
(14) The recesses 9b, 10d and protrusions 11d, 11g need not be provided
symmetrically with respect to the central axis of the rotary shaft 5, and
need not be provided in pair.
The present invention should not be limited to the disclosed embodiment and
modifications but may be implemented in many other ways without departing
from the spirit of the invention.
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